This invention relates generally to wafer handling and more particularly to an improved wafer handling system.
Processing machinery for handling semiconductor wafers is known. Such machinery typically includes the ability to lift and spin the wafers to bring them in proximate distance to testing machinery. It is generally desirable to move the wafers as quickly as possible while keeping the plane of the wafer as flat as possible. While platters and other support mechanisms have been used, increasingly there is a need to handle the wafers by the edges so that both surfaces are accessible.
Handling wafers by the edges has involved compromise among the security of the grip, the speed at which the wafer may be moved and the degree of flatness exhibited by the wafer. The wafer can be securely gripped by increasing the inward force of each finger gripping. However, this action may deform the wafer and cause processing errors due to the distorted profile of the wafer. When a wafer is spun, the centrifugal forces act on the finger grippers. These forces tend to pull the finger grippers away from the wafer. If the pull on the gripper is sufficient, the wafer may slip in the grip causing erroneous measurements or the wafer may be released causing destruction of the wafer. Previous efforts to reduce this effect have included adding additional spring force to grip more tightly and compensate for the centrifugal force. However, this extra force can cause the previously noted deformation. Alternately, an upper speed limit can be placed on the rotation thereby limiting the centrifugal force. This limit slows the production line increasing manufacturing cost.
Thus there is a need to minimize and eliminate the undesired effect of centrifugal force on gripping fingers without distorting the shape of the wafer or allowing the wafer to slip within the grip.